Overcoming cancer is a major challenge of modern medicine. Living organisms are endowed with mechanisms to remove cancer cells and remain free of cancer. However, cancer does occur, and it presumably occurs when immunity weakens from some cause.
It is known that the blood of tumor-bearing mammals has increased levels of immunosuppressive proteins such as TGF-β and interleukin-10. It is thus considered possible to improve immunity and suppress tumor growth if these immunosuppressive proteins could be removed by extracorporeal circulation with an adsorption column. Patent Document 1 reports an adsorbent that adsorbs TGF-β and other immunosuppressive proteins. Patent Document 2 describes enhancing cytocidal activity and preventing spread of tumor to lungs by the extracorporeal circulation of the blood from a tumor-bearing rat using a column filled with an adsorbent adapted to adsorb immunosuppressive proteins such as TGF-β1 and S100A8/A9.
Recent findings suggest that some of the white blood cells in the blood of a tumor-bearing organism are immunosuppressive. Such cells with immunosuppressive activity are identified as CD4+CD25+FoxP3+ regulatory T cells (Non-Patent Document 1), CD4+ and CD8+ regulatory T cells expressing latency-associated peptide (hereinafter, simply “LAP”) on cell surfaces (Non-Patent Documents 2 and 3), and myeloid-derived suppressor cells such as Gr1highCD11bhigh (Non-Patent Document 4).
These cells secrete high levels of immunosuppressive proteins such as TGF-β and interleukin-10, and removing these cells is considered important in cancer treatment, probably more so than removing the immunosuppressive proteins.
However, the immunosuppressive cells are not the only cells contained in the blood; blood contains large numbers of other white blood cells that serve to improve immunity. It is indeed not easy to selectively remove only the immunosuppressive cells that account for only about 10% of the total white blood cells. One way of adsorbing only the immunosuppressive cells is to use a bead column immobilizing antibodies against immunosuppressive cells. However, the column needs to be sterilized by heat or radiation in order to be used for treatment. By being protein, the antibodies denature in the sterilization procedure, and lose functions. To date, no method is available that can sterilize protein-immobilized materials, and no column is known that can remove the immunosuppressive cells from blood for treatment.